Dewaxing



Jan. 7, 1936.

o. a. PAYNE DEWAXING Filed Aug. 51, 1931 Donald E..- Dogma Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE DEWAXING of Indiana Application August 31, 1931, Serial No. 560,333

12 Claims.

This invention relates to the separation of wax from oils and it pertains more particularly to a method and apparatus for dewaxing heavy viscous hydrocarbon lubricating oils.

Lubricating oils, particularly the so-called motor base stocks, must be free from wax in order that they may flow at low temperatures. The wax in heavy oils maybe a mixture of parafiin and ceresin (petrolatum) waxes, particularly when it is a heavy distillate as distinguished from a steam refined residual oil. Wax is removed from oils by diluting them with naphtha, chilling them to 20 to 40 F., and mechanically separating the diluted oil from the wax which crystallizes therefrom at the low temperatures. The mechanical separation in the case of paraffin wax is usually by pressing or filtering, and the separation of petrolatum is usually by settling or centrifuging. In both cases the wax which is separated must undergo further purification for the removal of oil, this beingaccomplished by sweating, distillation, or other conventional processes. It is very difiicult, however,'to separate mixtures of petrolatum and paraffin from 011 because petrolatum clogs a filter and paraflin is sometimes difiicult to settle or centrifuge. A wax slurry contains entrained oil, which is exceedingly difiicult to remove. The object of my invention is to provide an improved system for removing paraflin-petrolatum mixtures from lubricating oils.

A further object of my invention is to provide an improved system for continuously separating wax from oil and oil from wax and to accomplish this separation at a minimum cost. A further object is to provide a system for effectively using a butane-propane diluent for obtaining low cold test lubricating oils without incurring a fire hazard. A further object is to provide a dewaxed oil of improved color.

A further object is to provide an improved settling chamber.

A further object is to provide an improved sys-- tem of heat exchangers, mixers, separators, condensers, etc., whereby maximum heat and power efficiency may be obtained and whereby the process may be easily controlled. Other objects will be apparent from the following detailed description.

In practicing my invention I utilize the remarkable and unexpected properties exhibited by liquefied light hydrocarbons of the propanebutane range. It has been found that when liquefied butane and propane is used as a diluent in the ordinary dewaxing process an entirely different crystal formation is obtained than when filter naphtha is used. Petrolatum separates out in fine crystals in the butane-propane diluent instead of as an amorphous fiocculent mass as in filter naphtha. These fine crystals may be settled to yield a clear, cloudless diluted oil in about three or four hours, while the amorphous filter naphtha precipitate requires about 48 hours for settling. Furthermore, paraflln wax crystals may be separated by settling with the petrolatum crystals and it has been found that the pour point of the oils obtained are nearer to the temperature of dewaxing than when the ordinary processes are used; in other words the propanebutane dewaxing lowers the pour point differential. It has also been found that the crystal formation depends somewhat upon the rate and method of cooling and that this may be readily accomplished and controlled by the direct vaporization of the propane and/or butane in contact with the diluted oil-wax mixture. My invention utilizes all of these phenomena and my system may be briefly outlined as follows:

Waxy oil diluted with a butane-propane mixture is chilled and settled in a long horizontal chamber, wax being continuously removed from the base of said chamber and clear diluted cloudless oil being removed from the top thereof. 1 The diluted oil is used to condense butane and propane and it is then flashed and stripped of diluent vapors. The wax mixture from the first settling chamber is mixed with more propanebutane diluent and it is washed or preferably recrystallized in a second settling chamber, which is similar .to the first. The wax slurry removed from the second chamber is substantially oilfree,-the diluent is removed therefrom and returned to storage. The oil removed with the diluent in the second settling chamber is mixed, together with the diluent, with incoming waxy oil for introduction into the first settling chamber. It wilhthus be seen that I have provided a simple continuous system for effectively separating wax from oil. The invention will be more clearly understood from the following description or a preferred embodiment.

In the accompanying drawings, Figure 1 is a fiow diagram with parts of the apparatus diagrammatically illustrated, and

Figure 2 is a transverse section through a settling chamber taken along the lines 2-! of Figure 1.

The diluent which I employ consists preferably of about equal proportions of propane and butane.

It should be understood. however, that these proportions may be varied within a relatively wide range from substantially all butane to substantially all propane and it should be also understood that all other normally gaseous hydrocarbons, such as ethane, butylene, propylene, etc. may be present in smaller amounts; in fact pentane may in some cases be admixed therewith. The term butane includes both normal and isobutane, preferably the latter because its boiling point is nearer to that of propane.

The oil to be dewaxed may be a treated or untreated motor base stock or other viscous hydrocarbon oil, it being understood that the amount and nature of the diluent will necessarily vary with the nature of the oil to be dewaxed. In the preferred example I will describe the dewaxing of a motor base stock prepared from Midcontinent crude, this stock being an overhead distillate having a flash point of about 470 F., and a viscosity at 210 F. of about 70 to '75 seconds Saybolt. I prefer to design my unit to handle about 1,000 barrels per day of finished oil, which means that about 6,000 barrels per day of liquids must be circulated through the settling chambers. I prefer to mix about one part of oil with about 4 or 5 parts of the propane-butane mixture, so that the diluted oil in the settling chamber will have a sufliciently low specific gravity and viscosity to permit rapid settling.

Referring more particularly to Figure l, a waxy oil from storage tank I is withdrawn through discharge heater II, pump I2 and pipe I3 to mixer I4 where it is mixed with propane and butane from line I5. The waxy oil may be at a temperature of from 80 to 150 F. and the diluent mixture entering through line I5 may likewise be heated to effect complete solution of the wax and the diluted oil in mixer I4. This solution which may be at a temperature of from 100 to 140 F. is then transferred through pipe I6 and reducing valve II into settling chamber I8. Chilled diluent may be added to the mixture between reducing valve I! and the settling chamber or it may be introduced directly into the settling chamber by pipes I9. If it is introduced directly into the pipe, the introduction must be in such a manner that the desired crystal formation will be obtained,otherwise it should be introduced directly into the chamber.

The settling chamber I8 is preferably an elongated, cylindrical vessel horizontally mounted and provided with suitable baffles for maintaining desired chilling rates of the incoming mixture without disturbing the settling of the wax crystals. Preferably I provide plates I8a across the chamber near the inlet end, a space being left underneath the plates for the flow of liquids and a space being left above the plates for the passage of vapors. The settling chamber is, of course, heavily insulated since it is maintained at a temperature of -40 F.

At the base of the settling chamber I provide a trough which terminates in a closed pipe 2|. Both the trough and the pipe cooperate with an auger or screw 22 which is driven by motor 23 to force the wax slurry out of the settling chamber and through pipe 24 into wax sump 25.

Also at the end of the settling chamber opposite the intake I provide an overflow weir 26 for skimming the clear cloudless diluted oil which is then discharged through pipe 21 into dewaxed oil sump 28.

Chilling is effected by removing vapors from the settling chamber through pipes 29 and 30, valve 3 I, pipe 32, and compressor 33, which forces the compressed gases through pipe 34 and condensing coils 35 in receptacle 36, the condenser coils being connected by pipe 31 to the propanebutane storage tank 38. The temperature of the settling chamber I8 can be accurately controlled by regulating compressor 33. Bailies I8a are designed to retain the mixture for the first hour and the rate of cooling should be about 100 to 150 per hour, after which the mixture will be at about F. During the remainder of its fiow through the settling chamber some vapors may be removed from the surface of the liquid, but there will be substantially no agitation so that the wax crystals may rapidly settle to the bottom and be withdrawn by wax screw 22.

Propane-butane diluent from storage tank 38 is withdrawn through line 39, valve 40 and exchanger 4I to mixer 42, where it is mixed with a wax slurry introduced from pipe 43, chamber 44, pump a and pipe 45, which leads from the bottom of wax sump 25. This wax slurry gives up some of its heat in receptacle 44, as will be hereinafter described, and its temperature or the temperature of the incoming diluent may be so regulated that the temperature of the liquids in mixer 42 is high enough to redissolve the Wax in the propane-butane mixture. I may, of course, merely wash the wax crystals with cold diluent. but I prefer to purify them by recrystallization. This de-oiling of wax is commonly referred to in the art as repulping. The dissolved wax is introduced through pipe 46 and reducing valve 41 to settling chamber 48. I may introduce a part of the diluent through valve 48 and pipe 50 either into pipe 46 (subsequent to the reducing valve) or directly into the settling chamber 48.

This second settling chamber is likewise provided with baffles 480, for regulating the rate of cooling and for restricting the agitation to the end of the settling chamber. The chamber is cooled by the vaporization of diluent, the vapors being withdrawn through pipes 5| and 52, valve 53, pipe 32, compressor 33, etc. (these vapors are compressed and condensed with the vapors from settling chamber I8). A trough 54, pipe extension 55, wax screw 56 and wax screw driving motor 51 are provided for the removal of the wax slurry by means of pipe 58 into the second wax sump 59. This wax slurry is substantially free from oil but it must be separated from the propane-butane diluent. I therefore pass it through pipe 60, pump 6|, exchanger 62, heater 63 and pipe 64 into wax separator 65. This separator may be a cylindrical drum having suitable baflies or bubble plates to effect fractionation and stripping of the diluent vapors from the wax. The oil free wax is withdrawn from the base of the separator by pipe 66, passed through exchanger 62 and finally discharged through pipe The propane-butane diluent from separator 65 is withdrawn through line 68, condensed in coils 69 (immersed in vessel 44) and finally returned by pipe I0 and pump II to the storage system.

Clear propane-butane diluent containing a slight amount of oil flows over weir 12 in settling chamber 48. 'It is withdrawn through pipe I3 to oil diluent sump 14 from the base of which is passed through pipe 15, pump I6, pipe 11, valve 18, and exchanger I9 to pipe I5 for admixture with incoming waxy oil. I prefer to by-pass most of the oil diluent through valve and pipes I9, either to pipe I6 or directly to settling chamber I8, as hereinabove described. It is understood,

of course, that diluent may be introduced directly into pipe I! from storage chamber 38.

The finished oil from settling chamber I8 is withdrawn from oil sump by pipe 9| in pump 82 to condenser box 36 wherein it is used to condense the propane butane vaporsin coils 35. The cold diluted oil is then passed through pipe 84. condenser box 89, pipe 86, exchanger 81 and pipe 98 to oil separator 89, wherein the diluent is flashed from the oil and completely stripped therefrom. The wax-free oil leaves the base of separator 89 through line 99. The propanebutane diluent from the top of the oil separator II is passed through pipe 9|, condenser coils 92 (in condenser box 85) and pipe 93 to the propanebutane storage tank 38.

The operation of my invention is apparent from the above description and from the accompanying flow diagram. The propane-butane storage is preferably maintained at about '70 or 80 F. at which temperature it will have to withstand a pressure of about 30 to 150 pounds, depending upon the relative amounts of propane and butane in the diluent mixture. Both settling chambers are maintained at a pressure slightly less than atmospheric and at a temperature of about 20 to -40 F., it being understood that the temperature of the mixture is reduced after its introduc tion into the chamber at the rate of about 100 to 150 F. per hour. The settling chamber is so designed that during the continuous flow the oil is chilled for about one hour and is settled for about three or four hours. In other words, the volume of the settling chamber (up to the overflow weir 26) is about four or live times the hourly rate of flow of liquids therethrough. It should be understood, however, that a larger settling chamber may be provided and in any case the chamber should be relatively long and horizontal so that the wax crystals will not have to settle through an unduly long vertical distance.

In mixers l4 and 42 I prefer to effect complete solution of the wax in the diluted oil or diluent. If necessary I may pass steam through exchangers 4| and 19 respectively to raise the temperature of the liquids in the mixers to about 100 to 150 F. If the wax bearing streams are warm enough to be dissolved without the application of extra heat I will merely shut off the steam in these exchangers. It may be necessary to introduce an equal volume of diluent with the waxy liquid in the mixer, but I prefer to by-pass as much of the diluent mixtures as possible through pipes l9 and .59 respectively so that the bulk of the diluent will not have to be heated at the temperature of the mixer. It should be noted that the wax from the first sump 25 is melted and the propane-butane vapors from separator 65 are condensed in condenser box 44 and coils 69 respectively, and it should also be noted that the refrigerated dewaxed oil from sump 28 is effectively used to condense propane-butane vapors before it is flashed to separate the oil from the diluent.

While I have disclosed a preferred embodiment of my invention, it is understood that I do not limit myself to the details hereinabove set forth, except as defined by the following claims which should be construed as broadly as the prior art will permit.

I claim:

1. In apparatus of the class described, a closed horizontal settling chamber, means for continuously removing wax-free oil from a point near the top of the settling chamber. means for withdrawing diluent vapors from said chamber, means spaced from said wax-free oil discharge for introducing a diluted oil wax mixture, and means for restricting to one end of the chamber the agitation produced by the removal of vapors 5 from the incoming mixture.

2. In apparatus of the class described, an enclosed horizontal settling chamber. means for introducing a wax bearing oil and a vaporizable liquid at one end of said settling chamber, means 10 in said chamber for confining the agitation of the liquids to said end of the settling chamber whereby the liquids in the remainder of the settling chamber are substantially quiescent, means for removing a wax slurry from the base 15 of said chamber, means at the end of the chamber remote from the introduction of liquids for withdrawing wax-free diluted oil and means for withdrawing vapors from said settling chamber.

3-. In apparatus of the class described, a closed 20 settling chamber, means for dissolving a waxy oil in a light hydrocarbon diluent, means for introducing said solution into said settling chamber, means for separately withdrawing a wax slurry and dewaxed diluted oil from said settling chamber, means for dissolving said wax slurry in a diluent, a second settling chamber, means for introducing said solution of wax slurry and diluent into said second settling chamber, means for cooling both settling chambers to dewaxing 30 temperatures, means for separately withdrawing a wax slurry and a wax-free oil diluent from said second settling chamber, and means for introducing said wax-free oil diluent for admixture with said waxy oil.

4. The combination of claim 3 which includes means for withdrawing vapors from said settling chamber for effecting the refrigeration of liquids therein.

5. In apparatus of the class described, means 40 for mixing liquefied normally gaseous hydrocarbon diluent with wax-bearing oil, a closed elongated chamber, ,means for introducing the diluted wax-bearing oil solution into said chamber, means for removing diluent vapors at spaced 5 points along said chamber, means for allowing the wax to settle from the diluted oil without agitation, means for 'continuously removing waxfree diluted oil from the upper part and the wax slurry from the lower part of said settling chamber and means for continuously removing diluent from said wax-free oil.

6. The apparatus of claim 5 which includes a second settling chamber and means for repulping the wax slurry with fresh liquefied normally gaseous hydrocarbon diluent in said second settling chamber.

'l. The apparatus of claim 5 which includes a second settling chamber, means for repilping the wax slurry with fresh liquefied normally gaseous hydrocarbon diluent in said second settling chamber and means for returning the diluted oil solution from the repulping operation in the second chamber to said mixing means.

8. A method for removing wax from a waxhearing oil which comprises continuously introducing a solution of wax-bearing oil in a liquefled normally gaseous hydrocarbon diluent into a closed elongated cooling zone, removing vapors at spaced points along said zone, whereby the solution is chilled by the vaporization of the hydrocarbon diluent to cause the solidification of wax in readily separable form, continuously passing the cold diluted oil and solidified wax through a quiescent settling zone, continuously remov- 7 ing wax slurry from the base of the settling zone, continuously removing cold diluted wax-tree oil from the upper part of said settling zone and continuously removing the diluent from the dewaxed oil.

9. A method for removing wax from a. waxbearing oil which comprises continuously introducing ,a solution of wax-bearing oil in a liquefied normally gaseous hydrocarbon diluent into a closed elongated cooling zone, removing vapors at spaced points along said zone, whereby the solution is chilled by the vaporization of the hydrocarbon diluent to cause the solidification of wax in readily separable i'orm, continuously separating the wax from the diluted oil, and continuously removing the diluent from the dewaxed oil.

10. The process of claim 9 wherein the dewaxed oil solution is continuously passed in heat exchange relation to warmed diluent whereby the heat of the warmed diluent causes vaporization of diluent from the dewaxed oil solution and the refrigerative effect of the solution is used to cool the warmed diluent.

11. The process of claim 9 wherein the wax slurry is repulped with fresh liquefied normally gaseous hydrocarbon diluent for separating the entrained oil therefrom and wherein the repulp- 7 ing diluent containing said oil is used for dissolving the incoming wax-bearing oil.

12. The process of claim 9 wherein the dewaxed oil solution is continuously passed in heat exchange relation to diluent vapors whereby the heat 01! condensation of the vapors is utilized in 15 

